1. Field of the Invention
The present invention relates to an image forming apparatus, such as a color printer and a facsimile machine, and an image forming method for forming an image by using electrophotographic technology.
2. Description of the Related Art
Generally, an image forming apparatus (color printer) using electrophotographic technology is comprised of a photosensitive body, a charging means for charging the outer peripheral surface of the photosensitive body, an exposure unit for forming an electrostatic latent image by selectively exposing the outer peripheral surface of the photosensitive body, and a development unit for developing the electrostatic latent image into a toner image. Further, the image forming apparatus has a transfer unit for transferring the toner image onto a transfer object. A development rotary serving as a development unit holder, which has a substantially hollow cylindrical shape and is rotatably supported, is disposed at a position adjacent to the photosensitive body. The development rotary is formed in such a manner as to be capable of detachably installing development units of four colors (yellow Y, magenta M, cyan C, and black K).
However, with the image forming apparatus of the above-described conventional configuration, since four development units are installed to form a color image, the size of each development unit becomes smaller than the size of one development unit in an image forming apparatus for a monochromatic color. For this reason, if development, i.e., printing, is effected in monochrome in a large quantity by using the toner of one development unit in the image forming apparatus for forming a color image, a time when the toner is used up becomes early as compared with a case where an image forming apparatus for a monochromatic color is used.
Furthermore, the amounts of toners accommodated in the four development units are substantially the same. For this reason, in the case where monochromatic color printing is effected by using the toner of one development unit, a time when the toner used is used up becomes early as compared with the other toners. Accordingly, it is necessary to replace time and again the development unit of the toner used for the monochromatic color printing and replenish the toner, so that there has been a problem in that the replacement operation is very troublesome.
In addition, it was conceived to form the development unit used in monochromatic color printing to be larger than the development units of the other colors, so as to increase the amount of toner accommodated. In that case, however, there is a limit to the size in making the development unit large owing to such as the internal-structure of the color printer and the position where the development unit is installed. Additionally, a design change must be made in the shape of the development rotary to allow development units of different sizes, i.e., shapes, to be mounted, so that there has been a problem in that the manufacturing cost becomes high.